The overall objective of this proposal is to continue the support at Vanderbilt University of an interdepartmental, multidisciplinary Population Research Center. The continuous support of the Center maintains the efficiency of many population related projects now-active at Vanderbilt and permits development in new areas not presently represented. The research objectives of the Center include investigations on male reproductive physiology (sperm production, sperm biochemistry, sperm metabolism, sperm-maturation, sperm capacitation, and development of male contraception), on female reproductive physiology (fertilization and implantation), and on reproductive endocrinology (mechanism of sex hormone action, pituitary hormones, and prostaglandins). The Center grant supports an administrative core unit and seven core facilities (Hormone Assay, Histology and Photography, Electron Microscopy, Tissue Culture & Cytogenetics, Organic Chemistry, Cyclic Nucleotides, and prostaglandins).